1. Field of the Invention
This invention relates to the field of polymer compositions and, in particular, it relates to adhesive and coating compositions, adhesive-bonded fiberous articles, e.g. textile and non-woven materials, and to methods for manufacturing such materials.
2. Introduction
The field of textile and non-woven materials involves all manufactured forms of fiber assemblies including wovens, nonwovens, knitted articles, threads, yarns, ropes, bonded fiberous articles, such as mats, pads, diaper liners, all varieties of paper, tiles (e.g., acoustic tiles), etc. which are employed, in one form or another, in almost every aspect of commercial and household use, either alone or as components of composite articles. (For ease of reference, the term "textile," as used herein, includes bonded, non-woven, fiberous articles, such as papers, and fiberous mats, tiles and the like, as well as bonded woven and non-woven fabrics.) All of these utilities place one or more similar demands on textile materials. Almost without exception, the textile material must have adequate tensile strength for its intended purpose, and such strength is often required under both wet and dry conditions. The most common "wet" conditions to which textiles are exposed occur during manufacture, use, and cleaning and involve exposure to water, soap solutions, and/or dry cleaning solvents such as perchloroethylene. Textile materials exposed to flexing or tensile forces during manufacture, use, or cleaning require adequate flexibility, elongation (ability to stretch without breaking), and shape retention (ability to return to original dimensions after distortion). Since many textiles are exposed to wear during manufacture and use, they should possess adequate abrasion resistance, while those exposed to cleaning operations should have adequate scrub, solvent, and detergent resistance. Many textiles, such as clothing articles, drapes, and various household and commercial textiles, desirably have suitable "hand" (feel) for esthetic or utilitarian purposes. Many textiles also must be sufficiently stable, both chemically and physically, to heat, light, detergents, solvents, and other conditions of exposure to prevent variations in physical characteristics and/or discoloration, e.g. yellowing. Color stability, i.e., the retention of a textile's original color after exposure to heat, light, detergents, etc., is also desirable in many textile materials, particularly in those requiring esthetic appeal.
While all of these properties are, to a large extent, dependent upon the chemical composition of the fibers employed and their mechanical arrangement in the textile material, such properties can be, and often are, dependent upon the composition of chemicals, particularly polymeric binders, employed in their manufacture. Polymeric binders are widely employed to improve one or more physical properties of essentially all forms of textile materials. For instance, binders are used to improve shape retention, abrasion resistance, scrub resistance, and physical and chemical stability of woven and nonwoven textiles, knits, yarns, etc. The use of such binders to provide tensile strength as well as other desirable physical properties is a practical necessity in the manufacture of nonwoven textiles (also known as "formed" fabrics) which are usually characterized as webs or mats of random or oriented fibers bonded together with a cementing medium, such as starch, glue, or synthetic polymers. Synthetic polymers have largely displaced other bonding agents in the manufacture of nonwovens and other textile materials due primarily to improved physical properties they impart to the finished textile.
Synthetic polymers are typically applied to textile materials as solutions or as dispersions of the polymer in an aqueous medium. Such solutions and dispersions must, of course, possess properties which facilitate their use in textile manufacture. For instance, the solution or dispersion, as well as the polymer, must adequately wet the textile fibers to provide adequate distribution, coverage, and cohesiveness. Cohesiveness relates primarily to the ability of the polymer matrix to adhere to the textile fibers, particularly during manufacture and before curing has occurred. Rapid cure rate (the time required for the applied polymer to develop adequate strength in the textile material) is also important in manufacturing due to the demands of high speed manufacturing facilities. While curing catalysts, such as oxalic acid, are employed to cure some polymers, such as polymers which contain N-methylolamides, and they improve cure rate and physical properties, it is preferable, of course, to avoid the need for such catalysts. The necessity of catalyzing polymer curing increases cost and the technical complexity of textile manufacture and can result in the presence of undesirable toxic residues in the finished article.
The use of solvents other than water, while still widely practiced, is becoming more and more undesirable due to solvent expense and the costs and hazards involved in controlling solvent vapors. Yet solvents are still considered necessary to allow bonding of textile materials with polymers which cannot be employed in water-base systems. Thus, water-base polymer latexes are much preferred in the textile manufacturing industry, provided that the necessary physical and chemical properties can be achieved. However, substantial loss of one or more physical properties often results upon substitution of water-base latexes for solvent-base polymers. Latexes of polymers containing N-methylol-amide functional groups are known to improve physical properties in essentially all respects. However, such polymers release formaldehyde when cured, and they can result in formaldehyde residues in the finished product. Formaldehyde is coming under ever-increasing scrutiny in both the workplace and home; it is particularly undesirable in medical applications, feminine hygiene products, diapers, and similar articles. To illustrate, Japanese Law No. 112 of 1973 sets a maximum of 75 micrograms of formaldehyde per gram for all textiles used for any purpose and zero (non-detectable) for infant wear products. Similar laws have been proposed in the United States, and the state and federal Occupational Health and Safety Administrations (OSHA) have set stringent formaldehyde exposure limits for industrial workers. California Proposition 65 specifically identifies formaldehyde as a carcinogen and requires that labels for all products containing any amount of formaldehyde, i.e. even on the parts per million level, contain a caution statement that the article is carcinogenic. Thus, paper towels, diapers, and any other articles containing even miniscule amounts of formaldehyde must be labeled as carcinogenic. The necessity for assuring that formaldehyde is not present in manufactured articles is apparent.
Several rheological properties of water-base latexes are particularly important with regard to their utility in the manufacture of textile materials. For instance, control of latex particle size and particle size distribution is critical to the realization of desirable physical properties in many polymer latexes. Another factor, latex viscosity, can limit latex utility in textile manufacturing apparatus due to its influence on polymer distribution, filler loading, and fiber wetting.
Thus, it can be seen that the physical and chemical properties required in textile materials, and in the polymer solutions and dispersions employed to manufacture such materials, place various, sometimes conflicting, demands on the polymer system employed. Obviously, it is desirable to obtain a polymer system, preferably a water-base system, which possesses a wide range of properties desirable in the manufacture of textile materials.
Since cost of materials is always a factor in the production of manufactured articles, it is also desirable to provide polymer systems and manufactured articles, such as textiles, that are as inexpensive as possible, but which still possess the necessary physical and chemical properties. Obviously, cost can be reduced by employing less polymer in the manufacture of articles, such as textiles, although this, almost invariably, results in a loss of one or more desirable properties. While it is sometimes possible to extend polymer solutions, latexes or melts with relatively inexpensive materials, that practice almost invariably reduces one or more essential properties of the polymer system and of articles bonded with such polymers. The above-noted advantages of employing extended polymer compositions apply equally well to coating and adhesive compositions, and it is desirable to extend all types of coating and adhesive compositions with materials less expensive than the polymer itself with as little loss of desirable properties as is possible.